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Added uECC_generate_random_int(), and made uECC_vli_cmp() constant-time.

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This commit is contained in:
Ken MacKay
2015-10-12 21:29:56 -07:00
parent 41207c563a
commit 69744ae539
4 changed files with 69 additions and 38 deletions
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uECC.c
+46 -19
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@@ -139,9 +139,9 @@ uECC_VLI_API void uECC_vli_set(uECC_word_t *dest, const uECC_word_t *src, wordco
}
/* Returns sign of left - right. */
uECC_VLI_API cmpresult_t uECC_vli_cmp(const uECC_word_t *left,
const uECC_word_t *right,
wordcount_t num_words) {
static cmpresult_t uECC_vli_cmp_unsafe(const uECC_word_t *left,
const uECC_word_t *right,
wordcount_t num_words) {
wordcount_t i;
for (i = num_words - 1; i >= 0; --i) {
if (left[i] > right[i]) {
@@ -154,7 +154,7 @@ uECC_VLI_API cmpresult_t uECC_vli_cmp(const uECC_word_t *left,
}
/* Constant-time comparison function - secure way to compare long integers */
/* Returns one if left == right, zero otherwise */
/* Returns one if left == right, zero otherwise. */
uECC_VLI_API uECC_word_t uECC_vli_equal(const uECC_word_t *left,
const uECC_word_t *right,
wordcount_t num_words) {
@@ -166,6 +166,21 @@ uECC_VLI_API uECC_word_t uECC_vli_equal(const uECC_word_t *left,
return (diff == 0);
}
uECC_VLI_API uECC_word_t uECC_vli_sub(uECC_word_t *result,
const uECC_word_t *left,
const uECC_word_t *right,
wordcount_t num_words);
/* Returns sign of left - right, in constant time. */
uECC_VLI_API cmpresult_t uECC_vli_cmp(const uECC_word_t *left,
const uECC_word_t *right,
wordcount_t num_words) {
uECC_word_t tmp[uECC_MAX_WORDS];
uECC_word_t neg = !!uECC_vli_sub(tmp, left, right, num_words);
uECC_word_t equal = uECC_vli_isZero(tmp, num_words);
return (!equal - 2 * neg);
}
/* Computes vli = vli >> 1. */
uECC_VLI_API void uECC_vli_rshift1(uECC_word_t *vli, wordcount_t num_words) {
uECC_word_t *end = vli;
@@ -390,7 +405,7 @@ uECC_VLI_API void uECC_vli_modAdd(uECC_word_t *result,
const uECC_word_t *mod,
wordcount_t num_words) {
uECC_word_t carry = uECC_vli_add(result, left, right, num_words);
if (carry || uECC_vli_cmp(result, mod, num_words) >= 0) {
if (carry || uECC_vli_cmp_unsafe(result, mod, num_words) >= 0) {
/* result > mod (result = mod + remainder), so subtract mod to get remainder. */
uECC_vli_sub(result, result, mod, num_words);
}
@@ -553,7 +568,7 @@ uECC_VLI_API void uECC_vli_modInv(uECC_word_t *result,
uECC_vli_clear(u, num_words);
u[0] = 1;
uECC_vli_clear(v, num_words);
while ((cmpResult = uECC_vli_cmp(a, b, num_words)) != 0) {
while ((cmpResult = uECC_vli_cmp_unsafe(a, b, num_words)) != 0) {
if (EVEN(a)) {
uECC_vli_rshift1(a, num_words);
vli_modInv_update(u, mod, num_words);
@@ -563,7 +578,7 @@ uECC_VLI_API void uECC_vli_modInv(uECC_word_t *result,
} else if (cmpResult > 0) {
uECC_vli_sub(a, a, b, num_words);
uECC_vli_rshift1(a, num_words);
if (uECC_vli_cmp(u, v, num_words) < 0) {
if (uECC_vli_cmp_unsafe(u, v, num_words) < 0) {
uECC_vli_add(u, u, mod, num_words);
}
uECC_vli_sub(u, u, v, num_words);
@@ -571,7 +586,7 @@ uECC_VLI_API void uECC_vli_modInv(uECC_word_t *result,
} else {
uECC_vli_sub(b, b, a, num_words);
uECC_vli_rshift1(b, num_words);
if (uECC_vli_cmp(v, u, num_words) < 0) {
if (uECC_vli_cmp_unsafe(v, u, num_words) < 0) {
uECC_vli_add(v, v, mod, num_words);
}
uECC_vli_sub(v, v, u, num_words);
@@ -975,8 +990,8 @@ int uECC_valid_point(const uECC_word_t *point, uECC_Curve curve) {
}
/* x and y must be smaller than p. */
if (uECC_vli_cmp(curve->p, point, num_words) != 1 ||
uECC_vli_cmp(curve->p, point + num_words, num_words) != 1) {
if (uECC_vli_cmp_unsafe(curve->p, point, num_words) != 1 ||
uECC_vli_cmp_unsafe(curve->p, point + num_words, num_words) != 1) {
return 0;
}
@@ -1262,8 +1277,8 @@ int uECC_verify(const uint8_t *public_key,
}
/* r, s must be < n. */
if (uECC_vli_cmp(curve->n, r, num_n_words) != 1 ||
uECC_vli_cmp(curve->n, s, num_n_words) != 1) {
if (uECC_vli_cmp_unsafe(curve->n, r, num_n_words) != 1 ||
uECC_vli_cmp_unsafe(curve->n, s, num_n_words) != 1) {
return 0;
}
@@ -1319,7 +1334,7 @@ int uECC_verify(const uint8_t *public_key,
apply_z(rx, ry, z, curve);
/* v = x1 (mod n) */
if (uECC_vli_cmp(curve->n, rx, num_n_words) != 1) {
if (uECC_vli_cmp_unsafe(curve->n, rx, num_n_words) != 1) {
uECC_vli_sub(rx, rx, curve->n, num_n_words);
}
@@ -1358,14 +1373,11 @@ const uECC_word_t *uECC_curve_b(uECC_Curve curve) {
}
#if uECC_SUPPORT_COMPRESSED_POINT
/* Calculates a = sqrt(a) (mod curve->p) */
void uECC_vli_mod_sqrt(uECC_word_t *a, uECC_Curve curve) {
curve->mod_sqrt(a, curve);
}
#endif
/* Calculates result = product (mod curve->p), where product is up to
2 * curve->num_words long. */
void uECC_vli_mmod_fast(uECC_word_t *result, uECC_word_t *product, uECC_Curve curve) {
#if (uECC_OPTIMIZATION_LEVEL > 0)
curve->mmod_fast(result, product);
@@ -1374,9 +1386,6 @@ void uECC_vli_mmod_fast(uECC_word_t *result, uECC_word_t *product, uECC_Curve cu
#endif
}
/* Multiply a point by a scalar. Points are represented by the X coordinate followed by
the Y coordinate in the same array, both coordinates are curve->num_words long. Note
that scalar must be curve->num_n_words long (NOT curve->num_words). */
void uECC_point_mult(uECC_word_t *result,
const uECC_word_t *point,
const uECC_word_t *scalar,
@@ -1391,4 +1400,22 @@ void uECC_point_mult(uECC_word_t *result,
curve);
}
int uECC_generate_random_int(uECC_word_t *random, uECC_Curve curve) {
wordcount_t num_n_words = curve->num_n_words;
bitcount_t num_n_bits = uECC_vli_numBits(curve->n, num_n_words);
uECC_word_t tries;
for (tries = 0; tries < uECC_RNG_MAX_TRIES; ++tries) {
if (!generate_random_int(random, num_n_words, num_n_bits)) {
return 0;
}
if (!uECC_vli_isZero(random, num_n_words) &&
uECC_vli_cmp(curve->n, random, num_n_words) == 1)
return 1;
}
}
return 0;
}
#endif /* uECC_ENABLE_VLI_API */